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What is the difference between chromatids and chromosomes?

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jafrisaad89 | Student, Grade 10 | eNoter

Posted April 24, 2012 at 4:00 AM via web

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What is the difference between chromatids and chromosomes?

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jgeertz | College Teacher | (Level 1) Associate Educator

Posted April 24, 2012 at 6:45 PM (Answer #1)

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The difference between chromatids and chromosomes is subtle and can be confusing. We know that DNA is a double-stranded nucleic acid that holds the blueprint for cell growth, division, and function. DNA is arranged into chromosomes. In eukaryotic cells, chromosomes consist of linear strands, whereas in prokaryotic cells chromosomes are circle-shaped. Human beings have 46 chromosomes in each cell (23 from each parent). In order to fit this much DNA into each cell, it is packaged around histone proteins. A chromatin or DNA protein complex is the result. When cell division takes place, two identical copies of DNA are created by DNA replication. These two copies are connected by a centromere and the unit is termed a chromatid pair. A chromatid is one of the two copies or strands. Upon completion of cell division, each daughter cell ends up with one of the chromatids.

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bumbleberry7 | Student, Grade 9 | eNotes Newbie

Posted April 25, 2012 at 5:05 AM (Answer #2)

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The difference between chromatin, chromatid and chromosome

 

DNA, the blueprint of life, is organized into structures called chromosomes. In prokaryotic cells, chromosomes are circular, whereas in eukaryotic cells, they are linear strands. Different organisms have different numbers of chromosomes: human cells usually have 46 chromosomes, dogs have 78 chromosomes, while kangaroos have only 12 chromosomes!

This karyotype of a human male cell shows the 46 chromosomes.

The difference between chromatin, chromatid and chromosome

 

It’s easy to confuse these 3 terms! Let’s try to clear things up here.

DNA, the blueprint of life, is organized into structures called chromosomes. In prokaryotic cells, chromosomes are circular, whereas in eukaryotic cells, they are linear strands. Different organisms have different numbers of chromosomes: human cells usually have 46 chromosomes, dogs have 78 chromosomes, while kangaroos have only 12 chromosomes!

This karyotype of a human male cell shows the 46 chromosomes.

 

When you add all these chromosomes up, each cell actually contains about 2m of DNA! And all this DNA has to fit into a tiny nucleus of 5-10um in diameter. This is like trying to stuff a piece of string 2km long (it will take you about 20 minutes to walk from one end to the other) into a tiny bead smaller than 1cm!!! To do this seemingly impossible feat, cells devised an ingenious packaging system: it wraps DNA around proteins called histones. The resulting DNA-protein complex is called chromatin.

 

At the beginning of cell division (S-phase), the DNA is replicated, producing two identical copies of DNA, which are connected to each other at the centromere. This replicated X-like structure is now called a sister chromatid pair. A chromatid is therefore just one of the strands.

During mitosis, the sister chromatid pair condenses further, giving rise to the fat X chromosomes that you can see in the karyotype above. Therefore, chromosomes can be found in 3 forms: thread-like chromatin (during interphase), thread-like sister chromatids (during S-phase) and the condensed, visible form (during mitosis)

 

When a cell divides, the sister chromatids separate, and each daughter cell receives one of the strands. The chromatid then decondenses back into a long single chromatin strand when the new cell goes into interphase.

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